Why do electrons drift in an ideal conductor, since there's no field?Again, yes, the known superconductors have many other surprising and exotic properties that I would not expect from their definition. My understanding is that a "superconductor" is defined as "a conductor" (i.e., a material filled with movable electrical charges) "that has zero resistance" (i.e., electrical charges do not scatter). Do you have a better definition?

Jun23

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Why do electrons drift in an ideal conductor, since there's no field?@mgphys: Yes, real superconductors have many exotic and surprising properties. And yes, ballistic conduction does occur in non-superconductors. Are you implying that real superconductors are not filled with movable electrons that move without scattering? I would find that surprising, and would like to learn more.

What properties do you need for building a tower?Yes, your calculation shows that the free breaking length of a constant-cross-section carbon nanotube rope in constant 1g gravity is not quite long enough to reach from geostationary orbit all the way to the surface. However, all modern space elevator designs do not have constant 1g gravity, and are not constant-cross-section -- they are tapered.

Jan6

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What properties do you need for building a tower?How are "coal mines" relevant? My understanding is that most carbon nanotubes are produced from ethylene or methane, in turn purified from natural gas. The amount of carbon in a single year's production of ethylene -- 109 million tonnes in 2006 -- is over 4 orders of magnitude more than the 1,500 ton space elevator mentioned in the Space Elevator FAQ, which in turn is about 3 times the 400 ton weight of the international space station.

Why is an air conditioner more efficient in a low-thermal-mass house?In principle, that would be relevant if I ever wanted to "reduce the temperature (of the room) by an appreciable amount". However, in practice, every thermostat I've ever seen attempts to keep the temperature (of the room) the same. Or is there some connection between the temperature of the outside air (that the air conditioner cools off and blows into the room) and the thermal mass that I am missing?